No display

1. Laptop gets restarted when the it is connected to the mains. After switching off and on two or three times the computer comes to life. After hibernation display does not come back.
2. Desktop pc shows the motherboard details when starting and at the time of login to windows, the display goes off. There is no problem with the hard drive. I checked it with another computer using an enclosure.

I seek help for these two problems. Thank you.